The present invention concerns a device for actuation of the valves in reciprocating internal combustion engines.
For actuation of valves with a nonvariable valve stroke there are prior cam dwell linkages with three and more links, which are popular in today's reciprocating piston engines. For actuation of valves with variable valve stroke there are prior cam dwell linkages as well with four and more links (compare DE-OS 38 33 540 and PCT-FR 82/00221). All of these valves are actuated by cams which interact with a further link whose motion is transmitted to the valve through additional links.
Regarding the valve actuation devices for internal combustion engines as described in said patent disclosure, two aspects have evolved which are to be considered as worthy of improvement. One concerns the problem of the motion transmitted by the cam to the drive links, that is, to the tappets and the acceleration during the interval between the "closing" and "opening" of the valve. The other concerns a tribological problem, i.e., optimizing the intermediate link, typically a tappet, transmitting the rotary cam motion as a linear motion to the valves in terms of friction and lubrication. With an appropriate design of the mechanism, both partial problems can be solved in a device of the categorial type, resulting in an internal combustion engine with greater efficiency and extended service life.
As to the aforementioned problem regarding tappet acceleration, in the operation of the internal combustion engine, losing the contact between tappet and cam in the interval between "closing" and "opening" of the valve, i.e., when the valve is at rest, has proved to be disadvantageous in view of noise emission and material stress. This problem is not new though, and it has so far been solved by keeping the tappet in contact with the cam by means of a spring mechanism. However, this solution is not optimal in view of engineering expense and additional space needs.
Consequently, the problem underlying the invention is to improve cam follower linkages with three and more links such as used to drive the valves of internal combustion engines in view of noise emission and material stress without raising the engineering expense.
Regarding the problem of friction and lubrication, it has been demonstrated in view of the mechanism described in DE-OS 38 33 540 that increased friction occurs at the contact points between the intermediate link or tappet and the casing and of the intermediate link and output link during the valve closed period. Furthermore, the existence of unfavorable lubrication conditions due to the constant nonpositive connection at the contact point of the intermediate link and output link has been evidenced.